The present invention generally relates to a heating apparatus such as oven or the like. More particularly, the operation time and the inoperative time are counted using an operation equation to switch the magnitude of the thermal supply of the heating apparatus in accordance with the calculated values. The present invention is especially effective in a heating apparatus which combines a face heater comparatively large in thermal capacity with a heater having less thermal capacity, such as quartz tube heater.
Conventionally, in order to keep constant the temperature within the heating chamber, such as oven or the like, a thermistor is used to measure the temperature within the heating chamber. The temperatures are controlled to reduce or cut off the output of the thermal supply such as heater or the like and to energize the heater again. However, the use of the heat sensitive elements involved higher cost and required temperature adjustment of the heat sensitive elements, thus costing much manufacturing labor. Also, the atmosphere temperature of the food placed within the heating chamber caused a lag time due to the heater, the thermal capacity of the heating chamber, the thermal capacity of the food, and so on, so that some corrections are required.
In order to solve the above-described problems, a method of automatically correcting the baking time without the use of temperature sensitive elements is disclosed in Japanese Laid-Open Patent Application Tokkaisho No. 59-298124. This method has an energization storing means, which stores the energization time into the load had so far including the last time, the energization frequency and the non-energization time, to calculate the corrected value of the present energization item by the output of the energization storing means, to reduce the corrected value from the established set time to decide the present energization time so as to flow the current to the load for the decided time.
This method has disadvantages in that the number of the energizations is required to be stored, and more storing capacity is required though the temperature sensitive elements are not required to be used, and large errors are caused because of the number of the energizations, long, short, counted. Also, there is a large disadvantage in that it is impossible for a user to effect the heating operation for longer time, because the apparatus corrects the set time established by the user.
A second problem in the heating apparatus is the thermal-amount balance between a plurality of thermal supplies, for example, an upper-portion heating (a first thermal supply) and a lower-portion heater (a second thermal supply). Especially, when a quartz tube heater is used as a first thermal supply, a flat-shaped heater as a second thermal supply, only one of the heated is burned black with both the thermal supplies being energized for the same period of time, because the calorific amount, thermal capacity of both the thermal supplies, the distance to the heated are respectively different. In order to improve the disadvantages, a method of specifying the ratio of the energization time and effecting the heating operation is conventionally adapted to retain the energization ratio of the upper heater and the lower heater at a predetermined constant value is adopted. However, when the thermal amount of one heater is large, disadvantageously the temperature does not rise so easily. Also, keep large the energization amount to the heater large in thermal amount so as to oppositely quicken the rising speed of the heater temperature, and the difference in temperature between the upper, lower heaters is made large between the first time and the second time because of the large remaining heat of the heater. Even if the balance between the upper and lower heaters is good at the first time, only the single side is burnt at the second time inconveniently.
Also, as the type of foods is different in a toaster for baking bread and a pizza cooker for baking pizza, the output of the respective heaters is required to be charged. As before, the uniform heater output is not capable of handling each cooking menu.